Electronic postage meter systems have been developed, for example, the systems disclosed in U.S. Pat. No. 3,978,457 for MICROCOMPUTERIZED ELECTRONIC POSTAGE METER SYSTEMS, in U.S. Pat. No. 3,938,095 for COMPUTER RESPONSIVE POSTAGE METER, in U.S. Pat. No. 4,301,507 for ELECTRONIC POSTAGE METER HAVING PLURAL COMPUTING SYSTEMS, and in European Patent Application, publication No. 0 019 515 for ELECTRONIC POSTAGE METER HAVING IMPROVED SECURITY AND FAULT TOLERANCE FEATURES.
Each of the above electronic postage meters involves computing mechanisms which are physically sealed within tamper proof enclosures. This is because postage meters are adapted to print postage which have monetary value and both physical and electrical security must be provided to avoid tampering. As a result, a problem exist in energizing the electronic circuits of the meter within the secure postage meter housing in a way which will avoid intentional or inadvertent electrical damage or electromagnetic damage to the meter.
The electronic postage meters include non-volatile memory for storing critical information when power is not applied to the meter. Various types of accounting information may be stored in the meters non-volatile memory. This information includes, for example, the total amount of postage remaining in the meter for subsequent printing and the total amount of postage printed by the meter. Other types of accounting or operating data may also be stored in the non-volatile memory. Memory functions in the electronic postage meters have replaced the functions served in previous mechanical postage meters by mechanical accounting registers. These non-volatile memories, as well as volatile memories and other circuitry within the meter are susceptible to electromagnetic radiation and electrical transients which could either destroy information or cause erronious information to be generated. This can result in a loss of funds to the user. Accordingly, it has been recognized that various types of protection must be provided to avoid such undesirable results.